Technical Field
This disclosure relates to image, projection-based, additive manufacturing.
Description of Related Art
The surface finish of three dimensional objects made by image, projection-based additive manufacturing (AM) may be critical, such as for applications in optics, micro-fluid flow, and mechanical assembly, in which optical lenses, fluidic channels, and/or rotating components may all need to be smooth. However, there may be a stair-stepping effect in layer-based additive manufacturing processes in which a three-dimensional model is approximated by a set of two-dimensional layers. This may cause the fabricated surface to have a poor surface finish, especially when close to the horizontal plane.
FIG. 1 illustrates a layer-based additive manufacturing process and related stair-stepping effect. As shown in FIG. 1, a given three-dimensional (3D) model may first be sliced into a set of two-dimensional (2D) layers. By stacking these 2D layers together, a physical part can be fabricated in an AM process to approximate the original computer-aided design (CAD) model.
Due to the use of 2D layers, the fabricated part surfaces, especially ones whose normals are close to the building direction (Z axis), may have large approximation errors. Such poor surface quality may limit the use of AM in applications that require smooth surfaces, such as the fabrication of optical lenses, 3D micro-channels in microfluidic systems, and various assembly features in mechanism designs.
The approximation error may depend on the layer thickness used in the slicing of a 3D model. One approach for addressing the stair-stepping effect in AM may be to reduce the layer thickness. For example, the layer thickness typically used in a Stereolithography Apparatus (SLA) system may be 0.1 mm, while the layer thickness used in a recently developed inkjet-based systems (e.g. ones from Objet Geometries Ltd) can be as small as 0.012 mm.
While thinner layers may result in less stair-stepping problems, the use of such ultra-thin layer thickness may also significantly slow down the building process. In addition to a great sacrifice in building speed, it may be challenging for some AM processes to significantly reduce their layer thicknesses. For example, in the SLA process, the spreading of liquid resin into uniform ultra-thin layers can be difficult due to liquid viscosity.